The term “periodic breathing” describes a respiratory pattern in which clusters of breaths exhibit a waxing and waning of the amplitude of the tidal volume of ventilation in a cyclic pattern, typically with a period of one minute or less, causing the subject to oscillate between hyperpnea and hypopnea with a crescendo-decrescendo pattern. Cyclic patterns with periods greater than one minute typically indicate a high likelihood of impaired cardiac systolic or diastolic function. In a more extreme version the clusters of breaths may be separated by periods of apnea, instead of hypopnea. Frequently the hypopneic or apneic episodes of periodic breathing contain both obstructive and central events.
Although the exact cause of periodic breathing in adults has not been firmly established, it is thought that the cause may be related to excessive loop gain in the feedback control involved in the regulation of respiratory drive. In adults, periodic breathing is considered abnormal, and is often associated with subjects having neurologic dysfunction or heart failure.
During CPAP therapy, detection of periodic breathing is crucial, as it may be desirable to alter the therapy delivered to the subject if periodic breathing is present. For example, a normal reaction to the detection of an obstructive apnea may be to gradually raise the pressure delivered to the subject until the apneas are eliminated or converted to hypopneas. However, this rise in pressure can actually aggravate a periodic breathing respiratory pattern. Thus, it may be desirable to alter the treatment delivered by the device when periodic breathing is detected.
Current prior art devices are somewhat adept in detecting periodic breathing, but they lack sensitivity and the ability to distinguish between mild periodic breathing and severe periodic breathing. Therefore, it would be desirable to be able to detect periodic breathing with more sensitivity and to be able to distinguish between mild and severe periodic breathing such that delivered therapy may be adjusted accordingly.